The limited ability of anti-neoplastic therapy to distinguish neoplastic from normal cells continues to be a primary hurdle in the treatment and irradiation of neoplastic, tumor or other cancerous cells. Distinguishing between the two on the basis of proliferative behavior has shown some success, but the search for biochemical characteristics of neoplastic cells that are tumor specific rather than proliferation specific remains the focus of further research. Unfortunately current molecular genetic studies have failed to support the expectation that such characteristics are a consistent feature of neoplastic cells. Rather these studies suggest that the neoplastic state can be explained without postulating tumor specific functions, but merely the operation of normal proliferation-specific functions at abnormal levels, as a result of changes (sometimes minimal) in the structure of growth-regulatory genes or changes in their number or chromosomal environment. This conclusion suggests that continued search for highly specific attributes of neoplastic cells cannot be relied upon for a general solution to the problems of cancer therapy.
As can be seen there is a continuing need in the art for cancer therapy that specifically and selectively targets and kills cancer cells and their precursors.
In general, gene therapy for cancers and many diseases offers novel treatment strategies and leads to the destruction of malignant and suboptimal cells. Ideally, the goal in all cases is to target deregulated cells while leaving the surrounding cells healthy and intact. Major cancer therapy approaches have included chemosensitization, cytokine gene transfer, inactivation of proto-oncogene expression, replacement of defective tumor suppressor genes, and transduction of oncolytic viruses. Included in this category are Adeno-associated virus-derived vectors which have been shown to be nonpathogenic vectors with potential for cancer gene therapy.